2014 Annual Science Report

Arizona State University
Reporting | SEP 2013 – DEC 2014

Project Summary

We constrained conditions of formation of silica phases in putative aqueous systems within the Saturn’s icy moon Enceladus, and evaluated the composition of aqueous fluids formed during thermal evolution and rock dehydration of the dwarf planet Ceres.

4
Institutions

3
Teams

1
Publication

0
Field Sites

Field Sites

Project Progress

A detection of silica (SiO2) nano-size particles in the saturnian system with the Cassini spacecraft may indicate aqueous processes on the icy moon. Zolotov constrained physical-chemical conditions of silica formation in aqueous systems on Enceladus. The work shows that the concentration and speciation of Si-bearing solutes are mostly controlled by solubilities of secondary clay minerals in altered chondritic rocks. The concentration of dissolved SiO2 gradually increases with temperature and is not very sensitive to the pressure and redox state of the system. The work showed that aqueous alteration of carbonaceous chondritic materials forms fluids which are strongly undersaturated with respect to SiO2 phases, consistent with observations in chondrites. It was shown that cooled fluids remain undersaturated with respect to amorphous silica. Freezing or evaporation of SiO2-undesaturated chondritic fluids could be needed to precipitate silica phases. The detection of silica phases in the saturnian system indicates aqueous process within Enceladus but may not indicate high-temperature aqueous environments.

Zolotov and Mironenko modeled a global-scale non-isochemical alteration of the dwarf planet Ceres during its thermal evolution. They evaluated the phase composition in warmed Ceres’ interior, the upward transfer of fluids formed through dehydration of minerals, and the accumulation of water mantle (ocean). The calculations led to compositional and density profiles together with masses and volumes of all constituents (rocks, minerals, pore fluids, and water mantle) and the whole body. The models demonstrate the formation of a dehydrated rocky core surrounded by more hydrated and carbonated rocks. The forming ocean accumulates chemical species leached from rocks and released through alteration of minerals and organic compounds. This work showed that dehydration of Ceres’ interior could have been accompanied by redox transformations of organic compounds, reduction of sulfates, leaching of some elements (Na, C, S, etc.) from the rocks, and rock’s fracturing by overpressured gas-rich Na-C-Cl aqueous fluids. A downward freezing of the ocean could have led to accumulation of Na chloride and Na carbonate salts at the core-icy mantle interface. The evaluated fluid chemistry constrains habitability of putative aqueous phases within an early and today’s Ceres. The results will be presented at 46th Lunar and Planetary Science conference in 2015.

Anbar co-authored a publication with Chris McKay and Carolyn Porco that made the case for sampling and studying the Enceladus plume as prime target for astrobiology exploration. This paper was one of the 100 most read papers in Astrobiology in 2014.